A known water pump, which is applied to a water-cooled engine, includes an impeller (17) provided at an end of a rotational shaft (14) supported by a body (11) through a bearing (13), and coolant is circulated in the engine by rotating the rotational shaft (14). A space (19) is formed between the bearing (13) and a mechanical seal (18) provided between the impeller (17) and the bearing (13). Vaporized coolant drops leaking between the mechanical seal (18) and the rotational shaft are condensed in the space (19), and the condensed coolant drops are drained into a reservoir (22a) positioned at a bottom portion of the body (11) through a draining hole (22). A plug (23) which plugs up one side of the reservoir (22a) is provided at a side of the reservoir (22a). A vapor outlet (24), which establishes a communication between the reservoir (22a) and the atmosphere, is provided above the plug. An annular groove (27) is formed at the vapor outlet (24) along a sidewall of the reservoir (22a) (e.g., described in JPH11-336699A). Alternatively, a water pump includes the draining hole (22) having a stepped portion (22c) provided between the vapor outlet (24) and an opening plane (22b) of the draining hole (22) opening to the reservoir (22a), at which the vapor outlet (24) is positioned above the opening plane (22b). According to the foregoing water pump, the draining of the coolant leaking from the draining hole (22) to the atmosphere by running along a top surface of the vapor outlet (24) is prevented (e.g., JP2004-108250A).
However, a mechanical seal of water pumps has characteristics that there is a clearance between a rotational shaft and the mechanical seal, thus generation of leaks of the coolant unavoidably occurs, and thus when the coolant, leaked from the mechanical seal and condensed, is directly drained from the draining hole, a trace of coolant is marked on a body and on other parts. When antifreeze is used for coolant, alcohol components included in antifreeze adversely affect other parts, and coolant leaks are considered as a water pump failure.
Accordingly, with the construction of the water pump described above, leaked coolant is pooled in the reservoir through the draining hole so that the pooled coolant is discharged from the vapor outlet when a predetermined volume of the leaked coolant is reserved. Further, with the water pump described above, the annular groove is provided at the vapor outlet along the sidewall of the reservoir so that the leaked coolant runs along the top surface of the vapor outlet by surface tension to be drained to the atmosphere through the vapor outlet to be guided to the bottom of the reservoir. However, with the construction of the water pump described above, coolant may not be securely guided to the bottom of the reservoir and the reservoir may not be able to reserve adequate volume of the coolant. Possibly, there is a risk that the coolant may be drained to the outside without going through the groove which is supposed to guide the coolant to the bottom in case the leaked coolant is guided to the reservoir by running along the sidewall without dropping as drops from a wall surface at front side of the pump of an outlet to a drain. Further, in case the annular groove is provided along the sidewall of the reservoir, there is a risk that coolant may not be able to be guided to the bottom of the reservoir securely because the leaked coolant dries and adheres to the groove clogging the groove in doing so.
A need thus exists for a water pump, which securely reserves a predetermined volume of leaked coolant in a reservoir, and particularly at which the leaked coolant is not able to drain outwards by running along a sidewall of the reservoir.